Since plastic lenses are lighter, less fragile, and tintable, as compared with inorganic lenses, in recent years, the application of plastic lenses to optical elements such as spectacles lenses, camera lenses or the like has increased rapidly.
In particular, spectacles lenses have been required to have various features including optical properties such as (1) high refractive index and (2) low dispersion property (high Abbe's number), and being (3) excellent in heat resistance, (4) excellent in impact resistance, (5) easily tintable, (6) excellent in working properties such as cutting properties and the like. Accordingly, various resin materials for lenses have been developed and used until now.
Representative examples of those can be mentioned by polythiourethane-based resins (Patent Documents 1 and 2).
Among the polythiourethane-based resins, a polythiourethane-based resin obtained by using an isocyanate compound represented by the following Formula (1) (Patent Document 3) is used to provide a plastic lens having a high refractive index and low dispersion property, and exhibiting excellent heat resistance and impact resistance, thus it has been widely used for spectacles lenses.

Moreover, recent spectacles lenses are often subjected to processing such as subjecting the substrate of lenses to silicon hard coat treatment or inorganic non-reflecting coat treatment, thereby increasing the added value. However, it has been known that the impact resistance of the lens is deteriorated by subjecting such coat treatments. Particularly in United States, there is a case where a polythiourethane-based resin lens excellent in impact resistance is also subjected to a primer coat for improving an impact resistance before being subjected to a hard coat treatment, so as to meet the standard for impact resistance defined by the U.S. Food and Drug Administration (FDA). In consequence, further improvement of the impact resistance on the substrate has been desired (Patent Document 4).
Further, fashionability in spectacles lenses has been required recently, thus the demand in colored lenses has increased.
Herein, the tintability and the heat resistance of a substrate are usually in a trade-off relationship, and the tintability deteriorates when the heat resistance is far too high. In addition, when the heat resistance is lowered to improve the tintability, a problem arise in that cracks form on a coat upon the application due to the difference in heat resistance between aforementioned hard coat or non-reflecting coat and the lens substrate.
Consequently, a resin for lens exhibiting heat resistance at around 100 to 110° C., which is adequate in practical, and having excellent tintability has been demanded.
Hereinabove, a plastic lens is mentioned as an example, however, there has been demanded a polythiourethane-based resin with improved balance between optical properties, tintability, and resin strength.    [Patent Document 1] Japanese Patent Laid-open No. 2-270859    [Patent Document 2] Japanese Patent Laid-open No. 7-252207    [Patent Document 3] Japanese Patent Laid-open No. 3-124722    [Patent Document 4] Japanese Patent Laid-open No. 9-113852